The fastener of U.S. Pat. No. 3,695,324 has been used successfully for several years offering several advantages over conventional nutplates. The fastener assembly is held to the workpiece by upsetting the end of a tubular member to provide an attaching flange. This makes installation easier and quicker than conventional designs which use two rivets to hold the fastener in place, and requires forming only one opening in the workpiece. The fastener also allows for removal and replacement of the nut of the assembly in the event of damage to that element.
However, the fastener of U.S. Pat. No. 3,695,324 has met with objections in some installations. These center around the use of the straight knurl on the periphery of the sleeve which becomes embedded in the workpiece to prevent rotation of the fastener relative to the workpiece. The knurl can cause stress risers leading to premature fatigue failure. Also, the resistance of the fastener to torque loads imposed upon it is not as great as desired in all instances.